Method of cleaning vulcanizing molds



y 23, 1933- F. K. BEZZENBERGER 1,910,277

METHOD OF CLEANING VULCANIZING HOLDS Filed July 5. 1932 Patented May 23,1933 UNITED STATES FREDERICK K. BEZZENIBERGER, OF CLEVELAND, OHIO METHODOF CLEANING VULGANIZING MOLDS Application filed July 5,

This invention relates to the art 015% in the films of rubber containingmaterial which adheres to molds used in vulcanizing ru er articles. Moreparticularly, it relates to the use of powerful oxidizing agents, suchas chemicals which have t e proper y of disintegrating the adhering filmand removing it from the molds. The invention also relates to therejuvenation of the chemicals employed to remove the film.

Heretofore the film of rubber containing material which adheres stronglyto molds, especially metal molds used in vulcanizing rubber articles,has been removed by the application of a flame to the film and resultantburning of the latter. This method is tedious and expensive and mayinjure the molds.

According to the present invention, I am enabled to remove this stronglyadhering film from metal molds in a simple, cheap and expeditiousmanner. This method involves, broadly speaking, the subjection of thefilm to a solution containing one or more suitable chemicals capable ofchemically oxidizing the binding material in the film in such a manneras to result in substantially complete disintegration of the film, and,consequently, removal thereof from the mold or mold parts. I believe thechemical reaction which takes place by this method is essentially anoxidizing action with oxidation of the rubber parts of the film whichbind or hold together the fillers or other material therein, and thatthe rubber is more or less completely oxidized into carbon dioxide andwater, since little or no rubber residue remains after this treatment.

As illustrative of chemicals which have the foregoing properties, Imention chromic acid, potassium dichromate, the various clilorates,Wroxides, particularly sodlum peroxide afid 'h'ydnogen peroxide. Thesevarious substances vary stfiiewtt in their rapidity of action, in theircost and in 1932. Serial No. 620,812.

the matter of their recovery after such use. Accordingly, I prefer touse chromic acid with or without other chemicals, for its first cost isnot exorbitant and it may be recovered or rejuvenated and repeatedlyused without substantial loss or deterioration.

As a specific example of the manner in which I may carry out the presentprocess, I may state that a solution of chromium trioxide in water tothe extent of a concentration of about and at a temperature of about 210F. will, within a short time, for example about fifteen minutes, removefrom a mold substantially all the film material adhering thereto, afterwhich the mold may simply be rinsed in water, dried, and again used forvulcanization.

Obviously, difl'erent concentrations than the foregoing may be employed,and I have found that the film material may be removed with watersolutions of chromic acid in which the concentration ranges betweenabout 10% and about 70%, and likewise that the temperature range withinwhich the solution may be used may range from about 70 F. to about th ebp i l ip g oint,-that is to about 525 F. I do not wis however, to limitmyself to any particular concentration, inasmucp as rplativelyd lowgpncentrations may unr er cer ain con itions e uite satisfictory, Whlgiiild tifih -seaeiiiiziii i fi ef p aa i tiaaiaio point enincre'ased'a'cid activity of'the so ution is desired, the concentrationshould be correspondingly low, because the acid activity of an acid bodyis inversely proportional to the concentration. 011 the other hand, Ibelieve that the oxidizing capacity of the solution is greater with thehigher concentrations and accordingly I prefer to use a relatively highconcentration, which, generally speaking, should not exceed thatconcentration at which the chromic acid crystallizes out on the top ofthe solution. There is danger that such crystallized chromic oxide maybe lost by being removed from the bath along with the mold when thelatter 1s being taken out for washing and drymg. chromic acidconcentration of about 50% in a water solution has been found to beentirely satisfactory under most conditions.

The film, when treated as above outllned, disappears more or less in itsentirety. Apparently the reaction is that of progressive eliminationfrom the exposed surface of the film to the mold, for observations madeduring the progress of the process indicate a gradual thinning of thefilm, withfinal complete removal. I believe the action WhlCh takes placeis that ofoxidation of .,the rubber material in thefilm intosuchcompounds as carbon .dioxide and. water. and that the inorganic orother non-readily o'xldlzable ma- .terials in the film have no adherenceto themold and fall away from the mold and collect in the bath as soonas the binding material has been oxidized or otherwise dissipated andremoved. Inorganic and other foreign and non-readily oxidizablematerialsdo collect in the bath as aresult of this process. v

I may-add other chemicals to thechromic acid solution mm rate of thereaction, or for other reasons. For example, I may add 'sul huric acidand/or potassium dichromate or other oxidizing agents or catalyticagentsfi I have also found that the speed of the reaction of the chromicacid may be increased by making the mold part to be cleaned the anode inan electric circuit in which the solution forms the electrolyte, whileseparating the cathode and anode compartments by a suitable diaphragm. Ihave found that the chromium trioxideor chromic acid which is employedin cleaning molds as aforesaid, may be reduced during the cleaning.operation to chromium chromate. This compound may be .reoxidized tochromium acid by any one of several different methods. For example, itmay be oxidized and thus rejuvenated by treatment with hydrogen peroxideor by anodic oxidation. When the cleaning opera- 7 tion takes place inan electrolytic bath,'tihe nascent .cxygen liberated at the anode,whether or not the mold be the anode, serves to reoxidize any chromiumchromate present to chromium trioxide or chromic acid. Obviously, thechromium chromate may be reoxidized or rejuvenated outside of the tankin which the cleaning operation is performed,

and a convenient means of accomplishing this would be to treat thewithdrawn solution in the anode chamber of an electrolytic bath muchlike that shown in the drawing and then return the rejuvenated-liquidfor .further use in cleaningmoldsj- 1 r-i In the drawing accompanyingand arming a "part of this application, the figure showsdiagrammatically :a form of apparatus which may he used in carrying outthe presout process and in rejuvenating the chromic acid.

In the drawing, 1 designates a suitable tank provided with a porousdiaphragm 2, a suitable cathode 3, of inactive material such as lead, ananode 4 of suitable material. The mold 5 to be cleaned may be made theanode if desired. Pipes 6 may be used to conduct heated fluids thru thebath to heat the bath liquids.

A water solution of chromic acid, with or without a small amount of sulhuri acld 1s 1 i 'parnno eank 1, and a solution of a suitable material,such as caustic soda is lac d in the cathode compartment, and bot areheated to the desired temperature. The chemical reaction between thechromic acid and the film material proceeds independently of theelectrical current until substantially all the film material has beendistintegrated and removed ,from the mold. During this action thechromic oxide may be in part reduced to chromium chromate. When currentis flowing the chro mium chromate is reconverted into chromic acid bythe nascent oxygen liberated at the anode. Substantially the samecleaning and oxidizing action takes place when the mold his made theanode in the electrolytic bath, and the cleaning action is thusexpedited by the oxygen liberated electrolytically at its surface. I "4The voltage and amperage of the current employed may vary over a widerange, but should be used in accordance with well known electrochemicalprinciples. Gene'r ally speaking, the current will vary depending on thesize of the apparatus, the volume of liquid and the desired speed ofreaction. "In the event that the molds to be cleaned contain intersticesin which the presence of any chromic acid is objectionable, the moldsmay, after having been cleaned, be dipped or rinsed in a solutionof asuitablesubstance such'as barium hydroxide which will neutralize theeifect of or react with the chromic acid as in forming in theinterstices anins'ol 1 uble salt. The chromic acid not only acts toremove-the film from the'inold, but exerts an oxidizing action on themold surfaoes'a'nd hence renders the molds, particularly when made ofaluminum alloys, more resistant against corrosion. Y 'fil Since the moldwill carry with it some chromic acid when removed from the bath, it isdesirable to recover this acid. The mold with the acicl on it may berinsed with water and the acid and this rinse water maybe returned tothe bath. Since the temperature of the bath is preferablymaintainedquite high, the rinse water will rapidly evaporate and willnot materially dilute the acidin the bath. Having thus described myinvention that those skilled in the artmay be able'to practice the same,what I desire to secure b Letters Patent is defined in what is claimcc.

hat is claimed is:

1. The method of cleaning metal articles having a rubber containing filmadhering thereto, which includes the steps of exposing such a film to asolution containing chromic acid with other chemicals in an amountsufficient to oxidize chemically the binding material of the film,thereafter rinsing the mold.

2. The method of removing a film of rubber containing material adheringto a mold in which rubber articles have been vulcanized, which comprisessubjecting the film to a liquid containing chromic acid in an amountbetween about 10% and about concentration for a sufiicient time and asufiicient temperature for substantially complete oxidation of thebinding material of the film to take place with disintegration of thefilm, and then removing the mold from the contact with the liquid andrinsing and drying the mold.

3. The method of removing a film of rubber containing matter adhering toa mold in which rubber articles have been vulcanized, which comprisessubjecting the film to a liquid containing chromic acid amounting tobetween about 10% and about 70% conccntration and at a temperature ofbetween 70*- and about 225 F. until the binding material of the film hasbeen substantially disintegrated, and then removing the mold fromcontact with the liquid and rinsing the mold.

4. The method of removing film of rubber containing material adl'ieringto a mold in which rubber articles have been vulcanized, which comprisessubjecting the film to a liquid containing chromic acid to the extent ofabout 50% concentration at a temperature of about 210 F., until the filmhas substantially disintegrated, and then removing the mold from theliquid and rinsing the mold.

5. The method of cleaning metal articles having interstices and having arubber containin film adhering to the mold, which comprlses the steps ofsubjecting the film to a solution containing chromic acid in an amountbetween about 10% and 70% concentration and in such manner as to causesubstantially complete oxidation of the binding material of the film,with resultant disintegration of the latter, rinsing the mold and thenexposing the liquid remaining in the interstices of the mold to asolution capable of neutralizing the effect of the liquid in saidinterstices.

6. The method of cleaning metal molds having a film of rubber containingmaterial adhering thereto as a result of vulcanization, which comprisessubjecting the film to a liquid containing chromic acid to the extent ofbetween about 10% and 70% concentration at a temperature between about70 F. and

225 F. until the film has substantially disintegrated, and rejuvenatingthe chromic acid by subjecting the liquid to oxidation.

7. The method of removing the film of rubber containing matter adheringto the molds in which rubber articles have been vulcanized, whichcomprises disintegrating the film by exposing it to a solutioncontaining a sufiicient amount of chromic acid to oxidize chemically thebinding material of the film, subjecting the liquid to anodic oxidationand then employing the thus rejuvenated chromic acid for cleaning othermolds.

8. The method of removing the film of rubber containing materialadhering to molds in which rubber articles have been vulcanized, whichconsists in subjecting the film to a liquid containing between about 10%and about 70% chromic acid, constituting the mold an anode in anelectrolytic circuit of which the liquid is the electrolyte, and passinga current pf electricity through the mold and electrote. 9. Thecontinuous method of removing rubber containing material in the form ofa film adhering to molds in which rubber articles have been vulcanized,which comprises passing current through an electrolyte containingbetween about 10% and about 70% chromic acid, successively bringingmolds to be freed from such film into said electrolyte as anodes, andsubjecting the electrolyte to anodic oxidation, thereby maintaining itin active form.

10. The method of cleaning metal molds having a film of rubbercontaining material adhering thereto as a result of vulcanization, whichcomprises subjecting the film to a liquid containing chromic acid to theextent of between about 10% and 70% concentration at a temperaturebetween about 70 F. and 250 F. until the film has substantiallydisintegrated, and chemically oxidizing the chromium chromate in theliquid to chromic acid.

In testimony whereof I hereunto aflix my signature this 1st day of July,1932.

FREDERICK K. BEZZENBERGER.

